The present invention relates generally to optical amplifiers. More specifically, the present invention related to optical amplifiers with decreased insertion loss variations and to methods for controlling the insertion loss variation of optical amplifiers.
A typical terrestrially-deployed OFA (optical fiber amplifier) operates in a signal range of about 1530 nm to about 1560 nm, a region known as the xe2x80x9cconventionalxe2x80x9d or C-Band. It amplifies incoming optical signals, thus providing xe2x80x9cgainxe2x80x9d. The gain G is defined as the ratio of out-coming signal optical power to the in-coming signal optical power. Typical net OFA gain is about 25 dB, and the gain ripple (the gain excursion over the gain band) usually is about 0.5 to 1.5 dB. An OFA may comprise one or more coils of active fiber. The use of such multiple coils in optical fiber amplifiers adds complexity and leads to an increase in both the number of components and number of splices. With added complexity comes increased manufacturing variation among optical amplifiers of the same design as well as increased component insertion loss variation. That is, optical fiber amplifiers built to identical design, due to variation within tolerance limits, have different overall insertion losses. These variations affect OFA performance, with nearly a 1 dB change in gain ripple per 1 dB change in total amplifier insertion loss, an effect caused by a tilt in the gain spectrum (gain as a function of wavelength). Even for optical fiber amplifiers that utilize a variable optical attenuator, compensation of insertion loss variations arising from assembly may consume some of the range of the variable optical attenuator that can be used, otherwise, for some other purpose. In high-performance C-Band optical fiber amplifiers that do not contain a variable optical attenuator (VOA), the component and manufacturing insertion loss variations have to be mitigated in some other way in order to achieve the desired performance.
According to one aspect of the present invention, a method of providing a predetermined insertion loss in an optical fiber amplifier includes the step of utilizing a predetermined, fixed, spectrally-flat loss component (insertion loss pad, ILP) to bring total optical fiber amplifier insertion loss up to a predetermined fixed level.
According to another aspect of the present invention a method for assembling a plurality of optical amplifiers includes, for each amplifier, the following steps: (i) determining insertion loss requirement; and (ii) providing an insertion loss pad component, with a predetermined insertion loss matching the requirement for that amplifier, such that the insertion loss variation from amplifier to amplifier is less than 0.5 dB.
According to yet another aspect of present invention a method of providing padding insertion loss in an optical amplifier includes the step of utilizing a fixed loss, spectrally flat loss component which brings gain spectrum of said amplifier to a predetermined level.
It is an advantage of the present invention that it provides several methods for determining the value of the insertion loss of this ILP component.
For a more complete understanding of the invention, its objects and advantages refer to the following specification and to the accompanying drawings. Additional features and advantages of the invention are set forth in the detailed description, which follows.